netdev - Re: [Patch net] tipc: call start and done ops directly in __tipc_nl_compat

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Date:   Tue, 4 Sep 2018 19:39:20 +0800
From:   Ying Xue <ying.xue@...driver.com>
To:     Cong Wang <xiyou.wangcong@...il.com>, <netdev@...r.kernel.org>
CC:     <tipc-discussion@...ts.sourceforge.net>,
        Jon Maloy <jon.maloy@...csson.com>
Subject: Re: [Patch net] tipc: call start and done ops directly in
 __tipc_nl_compat_dumpit()


On 09/04/2018 10:12 AM, Cong Wang wrote:
> __tipc_nl_compat_dumpit() uses a netlink_callback on stack,
> so the only way to align it with other ->dumpit() call path
> is calling tipc_dump_start() and tipc_dump_done() directly
> inside it. Otherwise ->dumpit() would always get NULL from
> cb->args[0].

Thank you for your fix Cong!

Your solution is fine with me.

When we align __tipc_nl_compat_dumpit() with ->dumpit() functions
defined in tipc_genl_v2_ops[], cb->args[0] is used to save a
rhashtable_iter object allocated in tipc_dump_start(), and the object
will be retrieved with cb->args[0] in tipc_dump_done() and will be freed.

But unfortunately cb->args[0] has been used to other purposes in
tipc_nl_bearer_dump(), tipc_nl_node_dump_link(),
tipc_nl_name_table_dump(), tipc_nl_node_dump() and tipc_nl_net_dump().
It means cb->args[0] saved in __tipc_dump_start() will be overwritten in
these ->dumpit() functions. As a consequence, not only the
rhashtable_iter object allocated in tipc_dump_start() cannot be properly
released in tipc_dump_done(), but also more kernel panics might be
triggered in tipc_dump_done().

> 
> But, tipc_dump_start() uses sock_net(cb->skb->sk) to retrieve
> net pointer, the cb->skb here doesn't set ->sk, the net pointer
> is saved in msg->net instead, so introduce a helper function
> __tipc_dump_start() to pass in msg->net.
> 
> Fixes: 9a07efa9aea2 ("tipc: switch to rhashtable iterator")
> Reported-by: syzbot+e93a2c41f91b8e2c7d9b@...kaller.appspotmail.com
> Cc: Jon Maloy <jon.maloy@...csson.com>
> Cc: Ying Xue <ying.xue@...driver.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> ---
>  net/tipc/netlink_compat.c | 2 ++
>  net/tipc/socket.c         | 8 ++++++--
>  net/tipc/socket.h         | 1 +
>  3 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/net/tipc/netlink_compat.c b/net/tipc/netlink_compat.c
> index a2f76743c73a..82f665728382 100644
> --- a/net/tipc/netlink_compat.c
> +++ b/net/tipc/netlink_compat.c
> @@ -185,6 +185,7 @@ static int __tipc_nl_compat_dumpit(struct tipc_nl_compat_cmd_dump *cmd,
>  		return -ENOMEM;
>  
>  	buf->sk = msg->dst_sk;
> +	__tipc_dump_start(&cb, msg->net);
>  
>  	do {
>  		int rem;
> @@ -216,6 +217,7 @@ static int __tipc_nl_compat_dumpit(struct tipc_nl_compat_cmd_dump *cmd,
>  	err = 0;
>  
>  err_out:
> +	tipc_dump_done(&cb);
>  	kfree_skb(buf);
>  
>  	if (err == -EMSGSIZE) {
> diff --git a/net/tipc/socket.c b/net/tipc/socket.c
> index ab7a2a7178f7..a19b2b1c77ed 100644
> --- a/net/tipc/socket.c
> +++ b/net/tipc/socket.c
> @@ -3264,9 +3264,14 @@ int tipc_nl_sk_walk(struct sk_buff *skb, struct netlink_callback *cb,
>  EXPORT_SYMBOL(tipc_nl_sk_walk);
>  
>  int tipc_dump_start(struct netlink_callback *cb)
> +{
> +	return __tipc_dump_start(cb, sock_net(cb->skb->sk));
> +}
> +EXPORT_SYMBOL(tipc_dump_start);
> +
> +int __tipc_dump_start(struct netlink_callback *cb, struct net *net)
>  {
>  	struct rhashtable_iter *iter = (void *)cb->args[0];
> -	struct net *net = sock_net(cb->skb->sk);
>  	struct tipc_net *tn = tipc_net(net);
>  
>  	if (!iter) {
> @@ -3280,7 +3285,6 @@ int tipc_dump_start(struct netlink_callback *cb)
>  	rhashtable_walk_enter(&tn->sk_rht, iter);
>  	return 0;
>  }
> -EXPORT_SYMBOL(tipc_dump_start);
>  
>  int tipc_dump_done(struct netlink_callback *cb)
>  {
> diff --git a/net/tipc/socket.h b/net/tipc/socket.h
> index d43032e26532..5e575f205afe 100644
> --- a/net/tipc/socket.h
> +++ b/net/tipc/socket.h
> @@ -69,5 +69,6 @@ int tipc_nl_sk_walk(struct sk_buff *skb, struct netlink_callback *cb,
>  				       struct netlink_callback *cb,
>  				       struct tipc_sock *tsk));
>  int tipc_dump_start(struct netlink_callback *cb);
> +int __tipc_dump_start(struct netlink_callback *cb, struct net *net);
>  int tipc_dump_done(struct netlink_callback *cb);
>  #endif
>